Shock heat treatment of aluminum alloy articles

ABSTRACT

Processes for improving the strength of heat-treatable, age hardenable aluminum alloys, such as 6xxx, 2xxx and 7xxx aluminum alloys, are provided. The processes for improving the strength of heat-treatable, age-hardenable aluminum alloys involve a heat treatment step, termed “shock heat treatment,” which involves heat treatment at 200 to 350° C. that is conducted at a fast heating rate (for example 10 to 220° C./seconds) for a relatively short period of time (for example, for 60 seconds or less or for 5 to 30 seconds). In some examples, the shock heat treatment is accomplished by contact heating, such as heating an aluminum alloy article between complementary shaped heated dies of a press. Aluminum alloy articles, such as automotive panels, produced by the disclosed shock heat treatment are also provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. application Ser.No. 15/145,477, filed May 3, 2016, which claims the benefit of U.S.Provisional Patent Application No. 62/158,727, filed May 8, 2015, whicheach is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The invention relates to the fields of material science, materialchemistry, metallurgy, aluminum alloys, aluminum fabrication,transportation industry, motor vehicle industry, automotive industry,motor vehicle fabrication and related fields.

BACKGROUND

Heat-treatable, age hardenable aluminum alloys, such as 2xxx, 6xxx and7xxx aluminum alloys, are used for the production of panels in vehiclessuch as automobiles. These alloys are typically provided to anautomotive manufacturer in the form of an aluminum sheet in a ductile T4state (or temper) to enable the manufacturer to produce the automotivepanels by stamping or pressing. To produce functional automotive panelsmeeting the required strength specifications, the manufacturer has toheat treat the automotive panels produced from an aluminum alloy in T4temper to increase their strength and convert the aluminum alloy into T6temper. In automotive manufacturing, the heat treatment is oftenaccomplished for outer automotive panels during a paint bake process ofthe assembled motor vehicle body. For inner automotive parts, a separateheat treatment is often required, referred to as Post Forming HeatTreatment (“PFHT”).

Current processes used in the motor vehicle industry for heat treatmentof pressed aluminum automotive panels to increase their strength possessnotable disadvantages. Heat treatment during the paint bake cycle ofassembled motor vehicle bodies requires paint lines with sufficient heatpower to achieve the required temperature, particularly in thick andinner structural elements of a car. Paint bake heat treatment isdifficult, particularly for inner automotive panels, because the outerpanels act as a heat shield, resulting in uneven hardening of differentparts of a motor vehicle body. For example, during a typical paint bakecycle, the outer panels may be exposed to a temperature of 170 to 185°C. for about 20 minutes, which leads to their “bake” hardening. However,during a similar paint bake cycle, the floor panels in an assembledautomobile body are exposed to a temperature of only 130 to 160° C. for10 to 15 minutes, which does not result in significant hardening.Although effective, PFHT is inefficient. For example, a heat treatmentat about 225° C. for approximately 30 minutes may be required to getfull T6 temper in panels through PFHT. PFHT leads to high energy costs,is time consuming and requires expensive modifications of the productionlines. In other words, PFHT adds significant costs to and lengthensmotor vehicle production cycles.

SUMMARY

The invention provides aluminum alloy articles and related products andprocesses, which can be employed in the transportation industry or otherindustries for production of aluminum alloy parts, such as automobilepanels. More generally, the products and processes of the invention canbe employed in the fabrication of aluminum parts used in variousmachinery and mechanisms.

Covered embodiments of the invention are defined by the claims, not thissummary. This summary is a high-level overview of various aspects of theinvention and introduces some of the concepts that are further describedin the Detailed Description section below. This summary is not intendedto identify key or essential features of the claimed subject matter, noris it intended to be used in isolation to determine the scope of theclaimed subject matter. The subject matter should be understood byreference to appropriate portions of the entire specification, any orall drawings and each claim.

The terms “invention,” “the invention,” “this invention” and “thepresent invention,” as used in this document, are intended to referbroadly to all of the subject matter of this patent application and theclaims below. Statements containing these terms do not limit the subjectmatter described herein or to limit the meaning or scope of the patentclaims below.

Disclosed is an improved heat treatment process for aluminum alloyarticles produced from heat-treatable, age-hardenable aluminum alloys,such as 2xxx, 6xxx, and 7xxx aluminum alloys. The heat treatmentprocesses disclosed herein improve mechanical characteristics of analuminum alloy article being treated, for example, by increasing itsstrength. The improved heat treatment processes are significantlyshorter and use a very fast heating rate, in comparison with theprocesses currently employed in the automotive industry to heat treataluminum panels, such as PFHT. The improved heat treatment processes maybe carried out on alloys that are preaged or not preaged.

The disclosed heat treatment processes can be efficiently incorporatedinto production processes for motor vehicle parts, such as automotivealuminum alloy panels, and can advantageously replace PFHT in automotiveproduction cycles. At the same time, the aluminum alloy articles treatedby the improved heat treatment processes are capable of achieving thestrength characteristics comparable to those achieved by the use ofPFHT. The disclosed heat treatment processes, which may be referred toas “shock heat treatment,” can be easily incorporated into the existingautomotive production lines used for manufacturing pressed aluminumpanels. For example, shock heat treatment stations can be incorporatedinto the press line of the automotive panel production line to produceheat treated aluminum automotive panels in T6 or T61 temper. The term“T61 temper” is used to denote an intermediate temper between T4 and T6,with higher yield strength but lower elongation than a material in T4temper, and with lower yield strength but higher elongation than in T6temper. The term “T4 temper” refers to an aluminum alloy producedwithout intermediate batch annealing and pre-aging. In addition, theautomotive panels may be in the T8 temper. The term “T8 temper” is usedto denote an alloy that has been solution heat treated, cold worked, andthen artificially aged. The alloys used in the methods described hereinmay be preaged or not preaged.

While well-suited for heat treatment of automotive aluminum alloy panelsduring their production, the improved heat treatment processes are moregenerally applicable to heat treatment of various aluminum alloyarticles, such as stamped or pressed aluminum alloy articles, tomodulate their mechanical characteristics, for example, to increasetheir strength. The disclosed processes can incorporate shock heattreatment into the existing processes and lines for production ofaluminum alloy articles, such as stamped aluminum articles, therebyimproving the processes and the resulting articles in a streamlined andeconomical manner. In some examples, an improved heat treatment processis accomplished by contact heating using heated tools of appropriateshape to heat the pre-formed aluminum articles. In some examples, apre-formed aluminum article is subjected to multiple shock heattreatment steps, which may be conducted at different temperatures. Sucha combination of shock heat treatment steps achieves desired mechanicalproperties (for example, strength) of an aluminum article in a shortertime than conventional heat treatment processes. In one example,subsequent to a stamping step, a stamped aluminum alloy article can be,subjected to two or more different contact heating steps at twodifferent temperatures. In another example, subsequent to a stampingstep, different parts of a stamped aluminum alloy article can besubjected to local contact shock heating steps to obtain differentstrength properties in different parts of the aluminum alloy article.Also disclosed are the aluminum alloy articles produced by the improvedheat treatment processes, such as motor vehicle aluminum alloy panels.Uses of the resulting automotive aluminum alloy panels for fabricationof motor vehicle bodies are also included within the scope of theinvention.

Some exemplary embodiments are as follows. One non-limiting example is aprocess for increasing the strength of a shaped aluminum alloy articleproduced from an age-hardenable, heat-treatable aluminum alloy,including heating one or more times at least a part of the shapedaluminum alloy article produced from the age-hardenable, heat-treatablealuminum alloy to a heat treatment temperature of 250 to 300° C. at aheating rate of 10 to 220° C./second, and maintaining the heat treatmenttemperature for 60 seconds or less. Another example is a process forproducing a shaped aluminum alloy article from an aluminum alloy sheetof an age-hardenable, heat-treatable aluminum alloy, the processincluding shaping an aluminum alloy sheet to form the shaped aluminumalloy article, heating one or more times at least a part of the shapedaluminum alloy article to a heat treatment temperature of 250 to 300° C.at a heating rate of 10 to 220° C./second, and maintaining the heattreatment temperature for 60 seconds or less. In the shaping step, theshaping may be shaping by stamping, pressing or press-forming thealuminum alloy sheet. In the above examples, the heat treatmenttemperature may be maintained for 5 to 30 or 10 to 15 seconds. Theage-hardenable, heat-treatable aluminum alloy may be a 2xxx, 6xxx or7xxx series aluminum alloy. The age-hardenable, heat-treatable aluminumalloy may be in T4 temper prior to the heating step and/or in T6 or T61temper after the heating step. The yield strength of the age-hardenable,heat-treatable aluminum alloy may increase after the heating step by atleast 30 to 50 MPa. The heating may be conductive heating. At least partof the shaped aluminum alloy article may be heated by application of oneor more heated dies of complementary shape. The shaped aluminum alloyarticle may be heated as a whole or in part. For example, one or moreparts of the shaped aluminum alloy article may be heated at the same ordifferent temperatures. The exemplary process may comprise at least twoheating steps at two different temperatures and/or for different timeperiods. For example, the process may comprise at least two heatingsteps at two different temperatures. The temperature of the secondheating step may be lower than the temperature of the first heatingstep. In the above processes, the shaped aluminum alloy article may be amotor vehicle panel, although it need not be. Another example is ashaped aluminum alloy form produced by the disclosed processes, such asthe exemplary processes discussed above. The shaped aluminum alloy formmay be a motor vehicle panel, such as an automotive panel or any othersuitable product. Yet another non-limiting example is the use of theautomotive panel for fabrication of a motor vehicle body.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic illustration of a process of stamping and heattreating an aluminum sheet.

FIG. 2 is a graph of temperature as a function of time for samples ofalloy AA6451 subjected to heat treatment by salt bath immersion (solidlines) or Collin® hot press (dashed lines).

FIG. 3 is a graph of R_(p0.2) as a function of time for samples of alloyAA6451 subjected to heat treatment by salt bath immersion and in aCollin® press.

FIGS. 4A-B are graphs of R_(p0.2) as a function of time for samples ofalloy AA6451 subjected to heat treatment by salt bath immersion (thetemperatures above 300° C.) or in a Collin® press (the temperatures of300° C. and below).

FIGS. 5A-B are graphs of R_(p0.2) as a function of time for samples ofan experimental alloy subjected to heat treatment in a Collin® press atvarious temperatures and for various time periods.

FIG. 6 is an illustrative two-step heat-treatment process conducted on asample of alloy AA6451, the process including heat treatment in aCollin® press and subsequent salt bath immersion heat treatment.

FIGS. 7A-B are graphs of R_(p0.2) as a function of time for samples ofalloy AA6451 (panel A) and of an experimental alloy (panel B) subjectedto various heat treatment processes.

FIGS. 8A-D are illustrations of crash tubes of an alloy treated by shockheat treatment (panels A and B) and an alloy in T4 temper (panels C andD) after a horizontal crash test.

FIGS. 9A-B are graphs of deformation energy and load as functions ofdisplacement for the alloys in the horizontal crash test.

FIGS. 10A-D are illustrations of crash tubes of an alloy treated byshock heat treatment (panels A and B) and an alloy treated withconventional heat treatment (panels C and D) after a vertical crashtest.

FIG. 11 is a graph of load and energy as functions of displacement forthe alloys in the vertical crash test.

FIG. 12 is a schematic of a bending performance test.

FIG. 13 is a graph of R_(p0.2) as a function of time for alloys treatedat different temperatures in a Collin® press or at differenttemperatures by hot air.

FIGS. 14A-B are graphs of R_(p0.2) as a function of time at differenttemperatures for preaged and non-preaged alloys in T4 temper and T4 with2% prestrain.

FIG. 15 is a schematic illustrating integration of shock heat treatmentin press line stamping.

DESCRIPTION

Disclosed are processes for improving the strength of heat-treatable,age hardenable aluminum alloys, such as 2xxx, 6xxx and 7xxx aluminumalloys often used for production of automotive panels. The processes forimproving the strength of heat-treatable, age hardenable aluminum alloysinvolve a heat treatment step, termed “shock heat treatment,” whichinvolves heat treatment at 200 to 350° C. that is conducted at a fastheating rate (for example, 10 to 220° C./second) for a short period oftime (for example, for 60 seconds or less, for 5 to 30 seconds or for 5to 15 seconds). Shock heat treatment processes disclosed herein improvethe strength of heat-treatable aluminum alloys by employing shorterheating times and faster heating rates, in comparison to theconventional heat treatment processes, such as PFHT, commonly employedin the automotive industry. In some examples, shock heat treatment isaccomplished by contact heating an aluminum alloy article between heateddies of a press, although other heating processes can be employed, asdiscussed further in more detail.

Due to the short heating times employed, shock heat treatment accordingto some examples can be advantageously incorporated in the productionlines and processes employed in automotive industry for manufacturing ofaluminum automotive parts, such as automotive body panels. The disclosedshock heat treatment processes are not limited to the automotiveindustry, or more generally the motor vehicle industry, and can beemployed in other industries that involve fabrication of aluminumarticles. In one example, a shaped aluminum alloy article (or a partthereof) is produced from an age-hardenable, heat-treatable aluminumalloy, such as 2xxx, 6xxx or 7xxx series aluminum alloy, and issubsequently heated one or more times to a temperature of 250 to 350° C.for 60 seconds or less. In another example, a process involves shapingthe article from an aluminum alloy sheet of an age-hardenable,heat-treatable aluminum alloy, for example, by stamping, pressing orpress-forming the aluminum alloy sheet, and subsequently heating thearticle one or more times to 250 to 350° C. for 60 seconds or less.Shock heat treatment is discussed in more detail below.

Shock Heat Treatment

Processes according to examples involve applying one or more shock heattreatment steps to an aluminum alloy article. Shock heat treatmentaccording to examples disclosed herein is a heat treatment conductedaccording to characteristic parameters, such as temperature, duration orheating rate, which can be used to describe the shock heat treatmentstep or steps. One of the characteristic parameters is a length of timeduring which the aluminum alloy article is held at an elevatedtemperature (i.e., soaking time), which can be, but is not limited to, 2seconds to 10 minutes, 60 seconds or less, 2 to 120 seconds, 2 to 60seconds, 2 to 30 seconds, 2 to 20 seconds, 2 to 15 seconds, 2 to 10seconds, 2 to 5 seconds, 5 to 120 seconds, 5 to 60 seconds, 5 to 30seconds, 5 to 20 seconds, 5 to 30 seconds, 5 to 15 seconds, 5 to 10seconds, 10 to 120 seconds, 10 to 60 seconds, 10 to 30 seconds, 10 to 20seconds or 10 to 15 seconds. Some of the exemplary shock heat treatmentsoaking times are about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55seconds, 1 minute (60 seconds) or 2 minutes (120 seconds). More than oneshock heat treatment step may be employed in a shock heat treatmentprocess. For example, in some cases, 2 to 5 shock heat treatment stepsof 5 seconds each may be conducted, resulting in a cumulative shock heattreatment time of 10 to 25 seconds. Each of the multiple heat treatmentsteps may be conducted for one of the durations specified above;different durations may be employed for different steps. In someinstances, the cumulative or combined length of the multiple shock heattreatment steps may be longer than the maximum soaking times specifiedabove. Conducting a heat treatment step over a relatively short timeperiod, such as 5 to 30 seconds, allows for efficient incorporation ofthe heat treatment step into certain fabrication processes andproduction lines, such as an automotive panel manufacturing line,without major disruption of such lines and processes. Shock heattreatment as disclosed herein can improve the mechanical characteristicsof an aluminum alloy that are at least comparable to the improvementsachieved by other heat treatment methods employing longer soaking times.

Shorter soaking times for shock heat treatment can be achieved bychoosing the temperature of the shock heat treatment so that the desiredchanges in the mechanical characteristics of an age hardenable aluminumalloy are modulated within a relatively short time period. Themechanical properties of an aluminum alloy achieved by employing shockheat treatment according to the methods disclosed herein can be tailoredby changing the temperature, time or both of the shock heat treatment.Shock heat treatment as described herein employs the exemplarytemperatures of 200 to 350° C., 200 to 325° C., 200 to 320° C., 200 to310° C., 200 to 270° C., 250 to 350° C., 250 to 325° C., 250 to 320° C.,250 to 310° C. or 250 to 270° C. For example, shock heat treatment maybe conducted at 250° C., 255° C., 260° C., 265° C., 270° C., 275° C.,280° C., 285° C., 290° C., 295° C., 300° C., 305° C., 310° C., 315° C.,320° C. or 325° C. By changing the temperature of shock heat treatment,one can modulate the mechanical characteristics, such as yield strength,of the resulting aluminum alloy or aluminum alloy article and/or therate at which these mechanical characteristics are achieved. Forexample, increasing the temperature of the shock heat treatment withinthe suitable range may lead to faster hardening of the aluminum alloy,characterized by a quicker rate yield strength increase. Thus, thebeneficial increase in yield strength of an aluminum alloy may beachieved in a shorter time. Higher soaking temperature can be employedto achieve more favorable kinetics of yield strength increase duringshock heat treatment. At the same time, increased temperature of theshock heat treatment may lead to lower peak yield strength, which shouldbe taken into account when choosing shock heat treatment temperature.Employing a combination of two or more heat treatment steps conducted atdifferent shock heat treatment temperatures, as discussed in more detailbelow, is one approach to achieving suitable mechanical characteristicsof an aluminum alloy or an article made from the aluminum alloy. Thechoice of the temperature or temperatures for one or more of the shockheat treatment steps also depends on the nature of an aluminum alloy,for example, its composition and treatment (which may be characterizedby temper) prior to shock heat treatment.

Shock heat treatment according to one example employs a heating rate of10 to 200° C./second, for example, 10 to 100° C./second, 10 to 50°C./second, 10 to 20° C./second. The heating rate can be achieved bychoosing an appropriate heating process or system to heat an aluminumalloy article. Generally, the heating process or system employed inshock heat treatment should deliver sufficient energy to achieve theabove-specified heating rates. For example, devices and processes forthermal conduction heating can be used to achieve a fast heating ratesuitable for the disclosed shock heat treatment. One example of such aprocess is contact heating of an aluminum alloy by heated tools of acomplementary shape. For example, for shock heat treatment, an aluminumalloy article can be treated by applying to the aluminum alloy articleone or more heated dies of a press having a complementary shape, asillustrated in FIG. 1. FIG. 1 is a schematic illustration of a processof stamping and heat treating an aluminum sheet. FIG. 1 shows a stampingpress 100 having two top dies 110 and two bottom dies 120 and shapedarticles 130 formed by compression between the top dies 110 and bottomdies 120. FIG. 1 further shows shaped articles 130 formed by thestamping press 100 placed in a heating press 200 having heated top dies210 and heated bottom dies 220. The heated top dies 210 and bottom dies220 are shaped such that they contact the surface of the shaped article130 without the dies 210, 220 changing the shape of the shaped article130. More generally, contact heating can be accomplished by any contactwith a heated object, substance, or body. Application of heated tools isone example. Another example of a contact heating process is immersionheating, which may involve immersing an aluminum alloy article in aheated liquid (“heated bath”). Shock heat treatment can also beaccomplished by non-contact heating processes, for example, by radiationheating. Some non-limiting examples of heating processes that can beemployed are hot air heating, contact heating, heating by induction,resistance heating, infrared radiation heating, and heating by gasburner. For example, a contact heating tool or tools of a suitable sizeand shape may be applied to a part or parts of an aluminum alloy articlein order to achieve local heating of the article's part or parts. Inother examples, a contact heating tool, such as a die of a heated press,may be applied to a whole article, or a heated bath may be employed toachieve heating of the whole article. In one more example, shock heattreatment may be performed only on a formed part of a previously stampedaluminum article, but not to its flange area, to maintainbending/hemming capability of the flange. Thus, for tailored shock heattreatment, design and optimization of the heating system and protocolmay be used to manage heat flow and/or to achieve the desiredcharacteristics of the treated article.

Shock heat treatment of an aluminum alloy article affects one or more ofthe mechanical properties of the aluminum alloy. The mechanicalcharacteristics of an aluminum alloy improved by the disclosed shockheat treatment can be one or more strength characteristics, such asyield strength, maximum tensile strength, and/or elongation. In someexamples, the strength of the age-hardenable, heat-treatable aluminumalloy is increased by one or more shock heat treatment steps. Forexample, yield strength of an aluminum alloy sample measured as 0.2%offset yield strength (R_(p0.2)) may be increased by at least 30 to 50MPa, for example, by 30 to 150 MPa or by 30 to 85 MPa. Differentmechanical properties of an aluminum alloy may be affected in differentways. For example, shock heat treatment under particular conditions mayachieve improvements in R_(p0.2) of an aluminum alloy comparable withthose achieved by heat treatment processes conducted for longer timeperiods, but the maximum tensile strength (R_(m)) and/or elongationachieved under these conditions may be lower than that achieved by thelonger heat treatment processes. In another example, if shock heattreatment is performed on an aluminum article after stamping, combinedeffects of strain- and bake-hardening may be achieved. Shock heattreatment conditions, such as the choice of temperature or temperaturesemployed and the number of shock heat treatment steps, are selected sothat they result in mechanical properties of an aluminum alloy suitablefor a particular application. For example, shock heat treatmentconditions employed in automotive panel fabrication are selected so thatthe resulting automotive panels possess suitable crash properties.

In some examples, more than one shock heat treatment step is employed.Two or more shock heat treatment steps conducted at two or moredifferent temperatures, for different time periods and/or at differentheated rates, can be employed to achieve desired strengthcharacteristics of an aluminum alloy. For example, two, three, four orfive shock heat treatment steps conducted at two or more differenttemperatures, for different time periods and/or at different heatedrates may be employed. A choice of shock heat treatment conditions, suchas temperature, heating rate, and/or duration, may affect theproperties, such as yield strength, of an aluminum alloy subjected toshock heat treatment or an article made from such alloy. For example,combining 2 to 5 shock heat treatment steps conducted on an aluminumalloy part at 250 to 350° C. (different shock heat treatment steps maybe conducted at different temperatures) for 5 seconds each results in acumulative shock heat treatment time of 10 to 25 seconds and achieve anincrease in yield strength of 30 to 150 MPa, depending on the nature ofthe aluminum alloy.

As discussed elsewhere in this document, higher shock heat treatmenttemperatures lead to faster increase in yield strength, thus allowingfor shorter shock heat treatment times, but may also lead to lowermaximum yield strength of the aluminum alloy subjected to shock heattreatment. Thus, a desirable combination of the aluminum alloyproperties can be achieved by manipulating the shock heat treatmentconditions and/or combining shot heat treatment steps. For example, aprocess combining one or more shock heat treatment steps conducted at ahigher temperature and one or more heat treatment steps conducted at alower temperature can lead to an alloy achieving higher yield strengthin shorter time, than a process employing shock heat treatment only atone of the temperatures.

In some examples, the first shock heat treatment step is conducted at ahigher temperature than the second shock heat treatment step. Forexample, the first step can be conducted at 300° C., while the secondheat treatment step can be conducted at 250° C. In another example,different parts of a stamped aluminum alloy article can be subjected todifferent local shock heat treatment conditions, employing, for example,contact heating tools of different temperatures, to obtain differentstrength properties in different parts of the aluminum alloy article.Furthermore, as discussed in more detail below, a combination ofmultiple shock heat treatment steps of shorter duration, rather than onelonger shock heat treatment step, may be employed for more efficientintegration of the shock heat treatment process into the lines andprocesses for production of aluminum alloy articles. The different shockheat treatment steps can be conducted by the same or different heatingmethods, at the same or different heating temperature, and/or for thesame or different durations of time. For example, a combination ofcontact heating by heating tools and heated bath treatment can beemployed. In cases employing two or more heat treatment steps, thesesteps can be employed simultaneously (for example, when local shock heattreatment of different parts of the article is employed), sequentially,or can overlap in time.

Aluminum Alloys and Aluminum Alloy Articles

Shock heat treatment as disclosed herein can be carried out with anyprecipitation hardening aluminum alloy (e.g., an aluminum alloycontaining Al, Mg, Si and, optionally, Cu, and capable of exhibiting anage hardening response). Aluminum alloys that can be subjected to thedisclosed shock heat treatment include age hardenable aluminum alloys,such as 2xxx, 6xxx, and 7xxx series alloys. Exemplary aluminum alloysthat can be subjected to the shock heat treatment may include thefollowing constituents besides aluminum: Si: 0.4 to 1.5 wt %, Mg: 0.3 to1.5 wt %, Cu: 0 to 1.5 wt %, Mn: 0 to 0.40 wt %, Cr: 0 to 0.30 wt %, andup to 0.15 wt % impurities. The alloys may include alternative oradditional constituents, so long as the alloys areprecipitation-hardening alloys.

The composition of an aluminum alloy may affect its response to shockheat treatment. For example, the increase in yield strength after heattreatment may be affected by an amount of Mg or Cu—Si—Mg precipitatespresent in the alloy. Suitable aluminum alloys for the shock heattreatment disclosed herein can be provided in a non-heat treated state(for example, T4 temper) or can be provided in a partially heat treatedstate (for example, T61 temper) and can be further heat treatedaccording to the disclosed processes to increase their strength. Thealloys may be preaged or not preaged. In some examples, theheat-treatable, age hardenable aluminum alloys subjected to the shockheat treatment are provided as an aluminum sheet in ductile T4 state oras articles formed from such sheet. The state or temper referred to asT4 refers to an aluminum alloy produced without intermediate batchannealing and pre-aging. The aluminum alloys subjected to shock heattreatment steps as disclosed herein need not be provided in T4 temper.For example, if an aluminum alloy is provided as a material that isartificially aged after stamping, then it is in T8 temper. And if thealuminum alloy is provided as a material that is artificially agedbefore stamping, then it is in T9 temper. Such aluminum alloy materialscan be subjected to shock heat treatment according to processesdisclosed herein. After shock heat treatment, the aluminum alloy sheetor the articles manufactured from such sheet are in T6 temper or partialT6 temper (T61 temper) and exhibit improvements in strengthcharacteristics associated with such tempers. As noted above, thedesignation “T6 temper” means the aluminum alloy has been solutionheat-treated and artificially aged to peak strength. In some otherexamples, the articles subjected to the shock heat treatment areinitially provided in partial heat treated state (T61 temper) and are inT61 or T6 temper after shock heat treatment. Even if the temperdesignation of the aluminum alloy article does not change after shockheat treatment, as in the case where the article is in T61 temper beforeand after the shock heat treatment, shock heat treatment still changesproperties of the aluminum alloy, for example, increases its yieldstrength.

Aluminum alloy articles suitable for shock heat treatment according tomethods disclosed herein include aluminum alloy articles formed orshaped from aluminum alloy sheets. An aluminum alloy sheet can be arolled aluminum sheet produced from aluminum alloy ingots or strips. Thealuminum alloy sheet from which the aluminum alloy articles are producedis provided in a suitable temper, such as T4 or T61 temper. Formed orshaped aluminum alloy articles include two- and three-dimensionallyshaped aluminum alloy articles. One example of a formed or shapedaluminum alloy article is a flat article cut from an aluminum alloysheet without further shaping. Another example of a formed or shapedaluminum alloy article is a non-planar aluminum alloy article producedby a process that involves one or more three-dimensional shaping steps,such as bending, stamping, pressing, press-forming or drawing. Such anon-planar aluminum alloy article can be referred to as “stamped,”“pressed,” “press-formed,” “drawn,” “three dimensionally shaped” orother similar terms. An aluminum alloy article can be formed by a “coldforming” process, meaning no additional heat is applied to the articlebefore or during forming, or by a “warm forming” process meaning thearticle is heated before or during forming, or the forming is conductedat elevated temperature. For example, a warm-formed aluminum alloyarticle can be heated to or formed at 150 to 250° C., 250 to 350° C. or350 to 500° C.

The aluminum alloy articles provided or produced by processes describedherein are included within the scope of the invention. The term“aluminum alloy article” can refer to the articles provided prior to theshock heat treatment, the articles being treated by or subjected to theshock heat treatment, as well as the articles after the shock heattreatment, including painted or coated articles. Since shock heattreatment can be advantageously employed in a motor vehicle industry,including automotive manufacturing, the aluminum alloy articles andprocesses of their fabrication include motor vehicle parts, such asautomobile body panels. Some examples of motor vehicle parts that fallwithin the scope of this disclosure are floor panels, rear walls,rockers, motor hoods, fenders, roofs, door panels, B-pillars, longerons,body sides, rockers or crash members. The term “motor vehicle” and therelated terms are not limited to automobiles and include but are notlimited to various vehicle classes, such as, automobiles, cars, buses,motorcycles, off highway vehicles, light trucks, trucks, and lorries.Aluminum alloy articles are not limited to motor vehicle parts; othertypes of aluminum articles manufactured according to the processesdescribed herein are envisioned and included. For example, shock heattreatment processes can be advantageously employed in manufacturing ofvarious parts of mechanical and other devices or machinery, includingairplanes, ships and other water vehicles, weapons, tools, bodies ofelectronic devices, and others.

Aluminum alloy articles disclosed herein can be comprised of orassembled from multiple parts. For example, motor vehicle partsassembled from more than one part (such as an automobile hood, includingan inner and an outer panel, an automobile door, including an inner andan outer panel, or an at least partially assembled motor vehicle bodyincluding multiple panels) are included. Furthermore, such aluminumalloy articles comprised of or assembled from multiple parts may besuitable for shock heat treatment according to methods disclosed hereinafter they are assembled or partially assembled. Also, in some cases,aluminum alloy articles may contain non-aluminum parts or sections, suchas parts or sections containing or fabricated from other metals or metalalloys (for example, steel or titanium alloys).

Processes and Systems

Processes of producing aluminum alloy articles can include one or moreof the steps discussed in this document. The aluminum alloy articles areproduced from an aluminum alloy sheet. In some cases, an aluminum alloysheet may be sectioned, for example, by cutting it into precursoraluminum alloy articles or forms termed “blanks,” such as “stampingblanks,” meaning precursors for stamping. Accordingly, the disclosedprocesses may include a step or steps of producing a precursor or ablank of an aluminum alloy article. The blanks are then shaped intoaluminum articles of a desirable shape by a suitable process.Non-limiting examples of the shaping processes for producing aluminumalloy articles include cutting, stamping, pressing, press-forming,drawing, or other processes that can create two- or three-dimensionalshapes. For example, a process can contain a step of cutting an aluminumsheet into “stamping blanks” to be further shaped in a stamping press. Aprocess can contain a step of shaping an aluminum alloy sheet or a blankby stamping. In the stamping or pressing process step, describedgenerally, a blank is shaped by pressing it between two dies ofcomplementary shape.

The processes disclosed herein include one or more steps of shock heattreatment. The processes may include shock heat treatment as astand-alone step or in combination with other steps. For example, theprocess can include a step of shaping an aluminum alloy article and oneor more steps of heat treating the shaped aluminum alloy articleaccording to the characteristic parameters (temperature, heating timeand/or heating rate) of shock heat treatment. The processes canincorporate shock heat treatment into the existing processes and linesfor production of aluminum alloy articles, such as stamped aluminumarticles (for example, stamped aluminum alloy automotive panels),thereby improving the processes and the resulting articles in astreamlined and economical manner. The apparatuses and the systems forperforming the processes and producing the articles described in thisdocument are included within the scope of the invention.

An example is a process for producing a stamped aluminum alloy article,such as a motor vehicle panel, which includes several (two or more, suchas two, three, four, five, six or more) steps of stamping the article ona sequence of stamping presses (“press line”). The stamping steps arethe so-called “cold forming” steps, meaning no additional heating of anarticle is performed. A stamping blank is provided before the firststamping step. The process includes one or more shock heat treatmentsteps conducted at different process points with respect to one or moreof the stamping steps. At least one of the shock heat treatment stepsmay be conducted on a stamping blank before the first stamping step(that is, at the entry of the press line). In this case, the blank,which may be provided in T4 temper, may be converted into T6 or T61temper after the above shock heat treatment step and before the firstpressing step. At least one shock heat treatment step may be performedafter the last stamping step (that is, at the end of the press line). Inthis case, the stamped article may be converted into full T6 temper bythe shock heat treatment step at the end of the line. Shock heattreatment steps may also be included after one or more of the first orintermediate pressing steps. For example, if the pressing line includesfive stamping presses and corresponding stamping steps, suchintermediate shock heat treatment steps may be included after one ormore of the first, second, third and fourth intermediate stamping steps.In the case when intermediate shock heat treatment steps are included,the article may be in T4 or T61 temper before an intermediate shock heattreatment step and may be in T61 or T6 temper after the intermediateshock heat treatment step. Shock heat treatment steps may be included ina production process in various combinations. For example, when one ormore of the intermediate shock heat treatment steps are employed, shockheat treatment steps may also be included at the beginning and at theend of the press line, as discussed above. Various considerations may betaken into account when deciding on a specific combination and placementof shock heat treatment steps in a production process. For example, if ashock heat treatment step or steps are introduced prior to a stampingstep or steps, forming by stamping may become more difficult, but it ispossible for the resulting article to retain higher strengthcharacteristics, in comparison to other configurations of the productionline.

The decisions on the duration and other parameters of the shock heattreatment steps, on the number and the integration points of the shockheat treatment steps and the corresponding stations to be included intothe fabrication processes or systems are made based on variousconsiderations. For example, as discussed earlier, a desirablecombination of aluminum alloy properties can be achieved by manipulatingthe shock heat treatment conditions. Accordingly, the decision on thenumber of shock heat treatment steps and their parameters can be basedat least in part on the desired properties of the aluminum alloyarticle. For example, longer shock heat treatment times may be moresuitable for achieving better crash properties, which may be desirablefor motor vehicle panels. Another decision-making consideration isefficient integration of the shock heat treatment steps into themanufacturing, fabrication or production process. For example, shockheat treatment steps of relatively short duration, for example, 5 to 20seconds or 10 to 20 seconds, may be integrated without major disruptionof the press line as intermediate steps conducted between the pressingsteps. On the other hand, a longer (for example, 30 to 60 seconds orlonger) shock heat treatment step may be more efficiently integrated asan additional step at the end of the press line. Based on the demands ofthe production cycle, in some cases a decision can be made in favor ofmultiple shock heat treatment steps of shorter duration to integratethem as intermediate steps. As discussed earlier, shock heating stepsintegrated into the process may be conducted at the same or differenttemperatures for different durations of time. For example, two or threeshock heat treatment steps or stations for heat treatment at differenttemperatures can be integrated into a production line for motor vehiclepanels. In one example, two heat treatment stations conducting shockheat treatments at 275° C. and 300° C., respectively, for 5 seconds eachare included into the production line for motor vehicle panels.

Shock heat treatment may be conducted on separate, dedicated equipment(system, station, machine or apparatus). Also disclosed are systems forproducing or fabricating aluminum alloy articles that incorporateequipment for shock heat treatment. One exemplary system is a press linefor producing stamped aluminum alloy articles, such as aluminum alloypanels, which incorporates shock heat treatment stations or systems atvarious points in the line, such as in the various examples discussedabove.

Shock heat treatment may be performed on assembled or partiallyassembled articles or parts. For example shock heat treatment may beperformed on motor vehicle parts, such as hoods or doors, after they areassembled. In another example, local or partial shock heat treatment maybe performed on fully or partially assembled motor vehicle bodies, forexample, by application of contact heating tools to a part or parts ofthe body. To illustrate, the parts of the assembled or partiallyassembled motor vehicle body that do not achieve sufficiently hightemperature during the paint bake cycle may be subjected to local shockheat treatment before or after the paint bake cycle to improve theirstrength. In such situations, a shock heat treatment step andcorresponding station may be integrated into a production line at somepoint during or after assembly of a motor vehicle part or body. Thechoice of the point on the assembly line for integrating a shock heattreatment can be governed by various considerations. For example, ashock heat treatment can be conducted after assembly of a motor vehiclebody to maintain best riveting ability of the body parts during theassembly. In another example, a shock heat treatment step can beincluded between any stage of the assembly of a motor vehicle body,including at a point governed by such non-limiting consideration asmaintaining the riveting or the joining ability of the body parts priorto the shock heat treatment.

The processes of producing or manufacturing an aluminum article asdisclosed herein can include a step of coating or painting an aluminumalloy article with suitable paint or coating. Usually, a shaped andshock heat treated aluminum alloy article is subsequently painted. Forexample, when the aluminum alloy article is used as an automotive orother motor vehicle panel, a body of the motor vehicle after assembly istypically coated and/or painted for corrosion protection and aesthetics.The paint and/or coatings may be applied by spraying or immersion. Afterapplication, the paint and/or coatings are typically treated in aprocess commonly termed “baking.” Processes disclosed herein may includea paint baking step, which can be referred to as “paint baking,” “paintbake,” “paint bake cycle” or other related terms. Paint bake typicallyinvolves heat treatment at 160 to 200° C. for a period of up to 1 hour,for example, for 20 to 30 min. Aluminum alloy articles can undergo apaint bake cycle or a comparable heat treatment cycle even without beingpainted or coated. For example, an unpainted and/or uncoated automotivepanel may be subjected to a paint bake cycle as a part of an assembledmotor vehicle body. As discussed elsewhere in this document, a paintbake cycle may affect the aging of an aluminum alloy from which thearticle is manufactured and thus affect its mechanical properties, suchas strength. Accordingly, a paint bake cycle or a similar heat treatmentstep may be employed in the processes described herein as an additionalheat treatment step, meaning that a process may comprise a paint bake ora similar heat treatment step in addition to the shock heat treatmentstep.

Advantages

The processes described herein are suitable, among other things, forfabrication of motor vehicle aluminum alloy panels and can replace PFHTin a motor vehicle production cycle. Shock heat treatment issignificantly shorter than PFHT and can be easily incorporated into theexisting motor vehicle production processes and production lines. Shockheat treatment is generally applicable to heat treatment of variousaluminum alloy articles, such as stamped or pressed aluminum alloyarticles, to increase their strength. Shock heat treatment canadvantageously replace conventional heat treatment steps employed duringproduction of aluminum alloy articles to increase their strength, or canbe used in addition to conventional heat treatment steps. The advantageof replacing a conventional heat treatment step, such as PFHT, with theshock heat treatment process as disclosed herein is that the shock heattreatment process can be one or more of: energy efficient due to theshorter heat treatment time; less time consuming; and/or easilyincorporated into an existing production process, for example,incorporated into an existing press line at production rate of the pressline. An advantage of such integration is that the press line can thenproduce the stamped or pressed aluminum alloy articles, such as motorvehicle panels, in T6 or T61 temper, which can enter the next processstep after the press line. Processes of shock heat treatment disclosedherein are also highly customizable, resulting in improved flexibilityof the production processes. For example, a shock heat treatment stepcan be easily and efficiently integrated into a motor vehicle productioncycle to produce desired characteristics of the article being produced,depending on demand.

The processes described herein increase the strength of the aluminumalloy articles subjected to shock heat treatment. In turn, the increasedstrength may allow for decreasing the thickness (down gauging) of thealuminum articles, such as automotive panels, thus decreasing theirweight and material costs. Furthermore, improved strengthcharacteristics of aluminum alloys achieved by the disclosed shock heattreatment can widen the use of aluminum alloys in various industries,such as the motor vehicle industry, particularly the automotiveindustry.

The following examples will serve to further illustrate the inventionwithout, at the same time, however, constituting any limitation thereof.On the contrary, resort may be had to various embodiments, modificationsand equivalents thereof which, after reading the description herein, maysuggest themselves to those skilled in the art without departing fromthe spirit of the invention.

EXAMPLES

In the following examples, sheets of aluminum alloy AA6451 and sheets ofan experimental alloy composition (referred to as “Alloy A” in thisdocument) were produced in T4 temper and in T4 temper with 2% pre-strainto imitate post-stamping conditions. Alloy A had a composition of 0.95to 1.05 wt % Si, 0.14 to 0.25 wt % Fe, 0.046 to 0.1 wt % Mn, 0.95 to1.05 wt % Mg, 0.130 to 0.170 wt % Cr, 0 to 0.034 wt % Ni, 0 to 0.1 wt %Zn and 0.012 to 0.028 Ti, remainder Al and impurities. The samples wereheat treated by a salt bath procedure and/or a hot press, or platenpress, procedure. For the salt bath procedure, the samples were heatedby immersion into a salt bath oven containing a molten salt mixture ofalkaline nitrates at a stable temperature. In the following examples,for the hot press procedure a Collin® press was used. The press washeated to a stable temperature, the samples were placed between twoplates of the press, and pressure was applied. The pressure ensured veryfast heating of the sample.

Example 1 Comparison of Heat Treating Methods

To compare the salt bath and hot press heating methods used in some ofthe following examples, samples of AA6451 were heated by the salt bathprocedure and by the hot press procedure. Data were collected with thesalt bath and the hot press each at 200° C., 250° C., and 300° C. Bothheat treatment procedures ensured fast heating of samples, asillustrated in FIG. 2. The solid lines in FIG. 2 demonstrate thetemperature of the sample heated by the salt bath procedure, and thedashed lines demonstrate the temperature of the sample heated by the hotpress procedure. The time required to achieve the target heat treatmenttemperature was approximately 15 seconds for the salt bath procedure andapproximately 5 seconds for the stamping procedure, as illustrated inFIG. 2.

The salt bath and hot press procedures provided comparable hardening ofthe alloy samples. The 0.2% offset yield strength (R_(p0.2)) of thesamples was measured to monitor the hardening process at temperatures of250° C., 275° C. and 300° C. for each heat treatment process, asillustrated in FIG. 3. The x-axis represents time the alloy is held atthe specified temperature. Heating time to the specified temperature isnot included, but it can be deduced from the data represented in FIG. 2as 15 seconds for the salt bath immersion and 5 seconds for the hotpress. FIG. 3 demonstrates that nearly identical alloy hardening isexpected using the salt bath and the hot press procedures. Therefore, inthe following examples, while only one procedure was used at eachtemperature, the results are exemplary of heating at that temperaturegenerally, irrespective of the heating method used.

Example 2 Yield Strength Achieved at Various Temperatures

Peak yield strength was determined at various temperatures by subjectingsamples of AA6451 and samples of Alloy A to heat treatment at varioustemperatures in the 200 to 350° C. heat treatment temperature range andmeasuring the 2% offset yield strength, R_(p2.0). FIGS. 4 and 5 showthat for both alloy AA6451 and Alloy A, while peak R_(p0.2) was reachedfaster at higher temperatures, the increase of the heat treatmenttemperature from 200° C. to 350° C. caused a decrease in peak R_(p0.2)for alloy AA6451 and Alloy A. The alloy samples were subjected to heattreatment by salt bath immersion for the temperatures above 300° C. andin a Collin® press for the temperatures of 300° C. and below. Thedifference in heating procedure at the different temperatures was aresult of limitations of the available equipment, and should not affectthe results, as Example 1 demonstrated that similar hardening isachieved by the two heating methods. In FIGS. 4 and 5, the x-axisrepresents the time the alloy is held at the specified temperature, notincluding the heating time.

FIG. 4A illustrates the experimental results for alloy AA6451 in T4temper subjected to heat treatment at various temperatures. Thehorizontal dashed line in panel A is a reference line indicatingR_(p0.2) achieved for the same alloy sample in T6 temper after heattreatment at 180° C. for 10 hours.

FIG. 4B illustrates the experimental results for alloy AA6451 in T4temper with 2% pre-strain subjected to heat treatment at varioustemperatures. The horizontal dashed line in panel B is a reference lineindicating R_(p0.2) achieved for the same pre-strained T4 alloy sampleafter a heat treatment of 185° C. for 20 min to put the alloy in T8Xtemper. As shown in FIG. 4B, for the AA6451 sample in T4 temper with 2%pre-strain, heat treatment for about 1 minute (total time in press) at275° C. led to R_(p0.2) of about 240 MPa, which is close to R_(p0.2)typically achieved during the simulated bake hardening process (heatingat 185° C. for 20 minutes) for the same alloy. Thus using a shock T6process, a part formed from this alloy that would not see a standardpaint bake, such as an inner part that is shielded by outer parts duringpaint bake, could reach the same strength as the paint baked parts fromthis alloy.

FIG. 5A illustrates the experimental results for Alloy A in T4 tempersubjected to heat treatment at various temperatures. The horizontaldashed line in panel A is a reference line indicating R_(p0.2) achievedfor the same alloy sample in T6 temper after heat treatment at 180° C.for 10 hours.

FIG. 5B illustrates the experimental results for Alloy A in T4 temperwith 2% pre-strain subjected to heat treatment at various temperatures.The horizontal dashed line in panel B is a reference line indicatingR_(p0.2) achieved for the same pre-strained T4 alloy sample after a heattreatment of 185° C. for 20 min to put the alloy in T8X temper. As shownin FIG. 5B, for the Alloy A sample in T4 temper with 2% pre-strain, heattreatment for 10 to 15 seconds (total time in press) at 300° C. led toR_(p0.2) of 300 MPa, which corresponds to R_(p0.2) typically achievedduring the simulated bake hardening process (heating at 185° C. for 20minutes) for the same alloy. Thus using a shock T6 process, a partformed from this alloy that would not see a standard paint bake, such asan inner part that is shielded by outer parts during paint bake, couldreach the same strength as the paint baked parts from this alloy.

Some of the R_(p0.2) increases achieved during the testing of heattreatment conditions are shown in Table 1.

TABLE 1 R_(p0.2) increases achieved during the testing of heat treatmentconditions Alloy Conditions R_(p0.2) increase AA6451, without pre-strain250° C., 30 seconds 30 MPa 275° C., 30 seconds 59 MPa 300° C., 10seconds 41 MPa AA6451, with 2% pre-strain 250° C. 30 seconds 38 MPa 275°C., 10 seconds 30 MPa 300° C., 10 seconds 31 MPa Alloy A, 250° C., 30seconds 44 MPa without pre-strain 275° C., 5 seconds 35 MPa 275° C., 10seconds 54 MPa 300° C., 5 seconds 67 MPa Alloy A, 250° C. 30 seconds 44MPa with 2% pre-strain 275° C., 5 seconds 35 MPa 300° C., 5 seconds 53MPa

Example 3 Combination Heat Treatment of Aluminum Alloy Samples

Samples of sheets of AA6451 and Alloy A were subjected to a two-stepheat treatment process, which included a Collin® press heat treatmentprocedure (10 or 30 seconds at 300° C.) and a salt bath procedure(various times at 250° C.), followed by air cooling. An exemplarytwo-step treatment process is illustrated in FIG. 6, which is a graph ofalloy sheet temperature as a function of time for a process of heating asample of AA6451 including heat treatment by Collin® press at 300° C.for 30 seconds, transfer to a salt bath, and heat treatment by salt bathat 250° C. for 20 seconds.

Samples of AA6451 and samples of Alloy A were subjected to variousone-step or two-step heat treatments. Samples of the alloys were heatedin a one-step heat treatment in a salt bath at 250° C.; a two-step heattreatment including Collin® press treatment at 300° C. for 10 seconds,followed by salt bath treatment at 250° C.; a two-step heat treatmentincluding Collin® press treatment at 300° C. for either 10 seconds or 30seconds, followed by salt bath treatment at 250° C.; or a one-step heattreatment in a Collin® press at 300° C. The x-axis represents the timethe alloy sample was held at each temperature, not including the heatingtime. As shown in FIG. 7, for both AA6451 and Alloy A, higher R_(p0.2)values were achieved by both of the two-step processes than by theone-step process at 300° C. R_(p0.2) increased much more quickly duringthe initial heating step (at 300° C.) of the two step processes and forthe one-step process at 300° C. than during the same time period for theone-step process at 205° C. But, R_(p0.2) increased more quickly duringboth of the two-step processes after switching to the second heatingstep at 250° C. than it did over the same time period during theone-step procedure at 300° C.

Example 4 Crash Tests for Shock Heat Treated Alloys

Crashability of an alloy sample treated by methods disclosed herein wascompared to a non-heat treated (i.e., T4 temper) sample of the samealloy. This alloy sample had a composition of Si 1.0, Fe 0.2, Cu 1.0, Mg1.0, Mn 0.08, Cr 0.14 all in wt %, up to 0.15 wt % impurities, with theremainder aluminum, and is referred to herein as “Alloy B.”

A sheet (2 mm thick) of Alloy B was heated in an oven at 500° C. for 90s (not including time to raise the sheet to 500° C.) to place the sheetin “Shock T6” temper. The sheet was then folded and bolted to form acrash tube. A second crash tube was formed from a sheet (2 mm thick) ofAlloy B in T4 temper. The tubes were tested in a quasistatic 3-pointbend setup (horizontal crash test).

FIG. 8 shows illustrations of the crash test tubes after the horizontalcrash tests. FIGS. 8A and 8B show the Shock T6 Alloy B. FIGS. 8C and 8Dshow the T4 Alloy B. As shown in FIG. 8, both tubes passed the test.FIG. 9 illustrates applied punch force (kN) and deformation energy (kJ)as functions of punch displacement (mm) for the horizontal crash tests.FIG. 9A is a graph of force and deformation energy as functions ofdisplacement for Alloy B in Shock T6 temper, and FIG. 9B is a graph offorce and deformation energy as functions of displacement for Alloy B inT4 temper. As shown in FIG. 9, the Shock T6 temper alloy absorbed 26%more energy than the T4 temper alloy (2.4 kJ as compared to 1.9 kJ).

These tests indicate that the materials treated by the methods disclosedherein have good crashability. The materials treated by methodsdisclosed herein absorb more energy during a crash compared to a T4material, but not quite as much as a standard T6 material.

Crashability of an aluminum alloy sample treated by methods disclosedherein and a sample of the same alloy treated by standard heat treatmentwere also compared. The alloy had a composition of 0.91 Si, 0.21 Fe,0.08 Cu, 0.14 Mn, 0.68 Mg, 0.04 Cr, and 0.030 Ti, all in wt %, up to0.15 wt % impurities, with the remainder aluminum, and is referred toherein as “Alloy C.”

A sheet (2.5 mm thick) of Alloy C in T4 temper was heated by shock heattreatment in a salt bath at 275° C. for 1 minute (not including 25seconds to raise the sheet to 275° C.) to place the sheet in “Shock T6”temper. The sheet was then folded and bolted to form a crash tube. Asecond crash tube was formed from a sheet (2.5 mm thick) of Alloy C inT4 temper. After forming, the tube was heated at 180° C. for 25 min toplace the tube in T62 temper as defined by ISO2107. The additionalheating conditions were chosen to give the T62 tube the same R_(p0.2) asthe Shock T6 tube, i.e., about 200 MPa. The tubes were tested invertical compression at a constant quasistatic speed in a press(vertical crash tests).

FIG. 10 shows illustrations of the crash test tubes after the verticalcrash tests. FIGS. 10A and 10C show side views of the crash tubes aftertesting, and FIGS. 10B and 10D show bottom views of the crash tubesafter testing. FIGS. 10A and 10B show the Alloy C Shock T6 tubes aftertesting. FIGS. 10C and 10D show the Alloy C T62 tubes after testing. Thecrash tubes in Shock T6 successfully folded upon crushing with notearing or cracks in the vertical crash test, whereas the referencecrash tubes exhibited some surface cracks in the areas 410 identified onFIG. 10C. Load and energy were measured as functions of displacement ofthe alloy material. FIG. 11 is a graph of load and energy as functionsof displacement for the Shock T6 and T62 materials illustrating that theShock T6 tube absorbed less energy during the crash test.

As compared to conventional heat treatment, shock heat treatmentresulted in an alloy with a lower ultimate tensile strength, as measuredby ISO 6892-1 but slightly better bending performance as measured by ISO7438 (general bending standard) and VDA 238-100 for similar R_(p0.2).FIG. 12 is a schematic of a bending performance test performed accordingto VDA 238-100. Table 4 summarizes the results of the tests.

TABLE 4 Shock T6 T62 R_(p)/R_(m) [MPa] 200/204 198/281 DC (alpha) [°]115 107 Crash ranking perfect good Crash Energy [kJ] 10.4 11.7

Example 5 Shock Heat Treatment Using Hot Air

Shock heat treatment with hot air can provide similar hardening to shockheat treatment with a hot press. Samples of Alloy A were heated using aCollin® press heated to 250° C., 275° C., or 300° C. or using hot air at350° C., 400° C., or 500° C.

FIG. 13 is a graph showing increase in R_(p0.2) as a function of timefor the samples heated using the different heating methods. R_(p0.2)increased more quickly with the hot press method, but similar maximumR_(p0.2)'s were reached using the hot air method in as little as about120 seconds.

Example 6 Shock Heat Treatment on Preaged Vs. Non-Preaged Materials

Preaged and non-preaged samples of AA6451 in T4 temper were shock heattreated in a Collin® press at 250° C. and 275° C. Preaged andnon-preaged samples of AA6451 in T4 temper with 2% prestrain were alsoheated in a Collin® press at 250° C. and 275° C. FIG. 14 shows the agingcurves of the samples. FIG. 14A shows R_(p0.2) (MPa) as a function oftime for the T4 materials, with “PX” indicating preaging, and FIG. 14Bshows R_(p0.2) as a function of time for the T4+2% prestrain materials,again with “PX’ indicating preaging. After the shock heat treatment,preaged T4 AA6451 treated at both 250° C. and 275° C. provided a higherstrength than the analogous non-preaged samples. Likewise, after theshock heat treatment, preaged T4 with 2% prestrain AA6451 treated atboth 250° C. and 275° C. provided a higher strength than the analogousnon-preaged samples.

Example 7 Integration of Shock Heat Treatment in Automotive ProductionProcess

Shock heat treatment steps may be integrated in a production line forfabrication of pressed automotive panels. The shock heat treatment stepsmay be integrated at any point where such treatment may be advantageous.For example, shock heat treatment steps may be integrated after apressing station, in one or more locations between presses in a seriesof pressing stations, and/or after the last press in the series. Oneexample of a production line is schematically shown in FIG. 15. Thesequence of presses is arranged as five pressing stations. Theproduction line illustrated in FIG. 15 includes up to five pressingstations (presses) needed to achieve the final shape of the panel.During an exemplary process, there is a waiting period before or betweenthe pressing stations due to the need to transfer the panels to thepressing station. One or more shock heat treatment steps may beimplemented during these waiting periods, as shown by the arrows 500 inFIG. 15. The length of time fits the stamping speed. In one instance,the shock heat treatment step is integrated into the production cycle byadding a contact heating station after the last pressing station. Inanother instance, the shock heat treatment step is integrated into theproduction cycle by adding a contact heating station between pressingstations four and five. In one more instance, several shock heattreatment steps are integrated into the production cycle by adding acontact heating station after each of the pressing stations or inbetween the pressing stations. The shock heat treatments are conductedfor 5 to 30 seconds at the contact stations integrated between thepressing stations. If a shock heat treatment step requires more than 30seconds, for example, 30 to 60 seconds, such a step is added at thecontact heating station integrated after the last pressing station.Integration of the shock heat treatment into the production line reducesproduction costs.

All patents, patent applications, publications, and abstracts citedabove are incorporated herein by reference in their entirety. Variousembodiments of the invention have been described in fulfillment of thevarious objectives of the invention. These embodiments are merelyillustrative of the principles of the invention. Numerous modificationsand adaptations thereof will be readily apparent to those of skill inthe art without departing from the spirit and scope of the invention asdefined in the following claims.

1. A heat-treated, shaped aluminum alloy article produced by: heating atleast one part of a shaped aluminum alloy article having one or moreparts, one or more times to a heat treatment temperature of 250 to 300°C. at a heating rate of 10 to 220° C./second; and, maintaining the heattreatment temperature for a time period of 60 seconds or less, whereinthe at least one part of the shaped aluminum alloy article comprises anage-hardenable, heat-treatable aluminum alloy.
 2. The article of claim1, further comprising: shaping an aluminum alloy sheet of anage-hardenable, heat-treatable aluminum alloy to form a shaped aluminumalloy article having one or more parts prior to heating the at least onepart of the shaped aluminum alloy article.
 3. The article of claim 1,wherein the shaping comprises stamping, pressing and/or press-formingthe aluminum alloy sheet.
 4. The article of claim 1, wherein the heattreatment temperature is maintained for 5 to 30 seconds.
 5. The articleof claim 1, wherein the age-hardenable, heat-treatable aluminum alloy isa 2xxx, 6xxx or 7xxx series aluminum alloy.
 6. The article of claim 1,wherein the age-hardenable, heat-treatable aluminum alloy is in T4temper prior to the heating step.
 7. The article of claim 1, wherein theage-hardenable, heat-treatable aluminum alloy is in T6 or T61 temperafter the heating step.
 8. The article of claim 1, wherein yieldstrength of the age-hardenable, heat-treatable aluminum alloy isincreased after the heating step by at least 30 to 50 MPa.
 9. Thearticle of claim 1, wherein the heating is conductive heating.
 10. Thearticle of claim 1, wherein the heating is by application of one or moreheated dies of complementary shape.
 11. The article of claim 1, whereinthe at least one part is the entire shaped aluminum alloy article. 12.The article of claim 1, wherein the at least one part is at least twoparts, and wherein the at least two parts of the shaped aluminum alloyarticle are heated at the same or different temperatures.
 13. Thearticle of claim 1, further comprising a second heating step at a secondheat treatment temperature for a second time period.
 14. The article ofclaim 13, wherein the second time period is different from the firsttime period.
 15. The article of claim 13, wherein the first heattreatment temperature and the second heat treatment temperature are twodifferent temperatures.
 16. The article of claim 15, wherein the secondheat treatment temperature is lower than the first heat treatmenttemperature.
 17. The article of claim 1, wherein the age-hardenable,heat-treatable aluminum alloy is a 2xxx, 6xxx or 7xxx series aluminumalloy.
 18. The article of claim 1, wherein the age-hardenable,heat-treatable aluminum alloy comprises Si from 0.4 to 1.5 wt %, Mg from0.3 to 1.5 wt %, Cu from 0 to 1.5 wt %, Mn from 0 to 0.40 wt %, Cr from0 to 0.30 wt %, and up to 0.15 wt % impurities.
 19. The article of claim1, wherein the article is a motor vehicle panel.
 20. A motor vehiclebody comprising the motor vehicle panel of claim 19.